The present invention relates to an electronic servo-control device for dental handpiece, of the type in which the vibration of a tool is obtained by means of a piezoelectric transducer.
It is known that a piezoelectric transducer generating ultrasound vibrations is, where possible, used in resonance so as to obtain maximum amplitudes and power of the vibrations. When such a transducer, to which a tool is mechanically coupled, comes into contact during a work phase with tissues of different natures, i.e. hard tissues, soft tissues, with or without the presence of a liquid, its resonant circuit evolves during the work. It is known that, in such a handpiece, the speed of vibration of the transducer is a direct function of the electric current which circulates therein and that the effort necessary for this vibration is a direct function of the supply voltage at the terminals of said transducer. It will be understood that, if it is desired that a handpiece operates with optimum yield, the vibrations of the transducer must correspond to the series resonance of this handpiece and, during work, the operational conditions must vary so as to remain in resonance.
According to the invention, the frequency will be tracked by observing the phase-shift which exists between the voltage and the current supplied and by electrically compensating the intrinsic capacity of the transducer. Such an electric circuit is translated in series resonance by a low impedance and a zero phase-shift.
The present invention thus has for its object to propose such a device for servo-control of the piezoelectric transducer of a vibration generator for dental handpiece, adapted to operate permanently at series resonance frequency, whatever the nature of the tissues on which the tool with which this handpiece is equipped, operates.
The present invention thus relates to a device for servo-control of a dental handpiece activated by an ultrasound generator, comprising supply means of given frequency, characterized in that:
it comprises two circuits, namely a work circuit to whose terminals the ultrasound generator is connected, and a control circuit,
the work circuit comprises an inductance in parallel between its output terminals,
the supply is adapted to deliver at the output a voltage in phase with a voltage which is delivered thereto on its input,
the control circuit is constituted by an intensity transformer whose primary is arranged in series in the work circuit and whose secondary forms, with a capacitor and a resistor associated therewith, an RLC circuit of which the voltage at the terminals of the resistor is sent to the input of said supply,
the control circuit comprises means for varying the value of the capacitor and/or that of the self-induction coil of the secondary of the intensity transformer.
The secondary of the intensity transformer preferably comprises a core mobile inside its winding adapted to vary its inductance.
In a preferred embodiment, the supply means will be connected to the work circuit via a voltage transformer of which the inductances of the primary and of the secondary will be high.
In an interesting form of embodiment of the invention, the inductance arranged between the output terminals of the work circuit will be such that, with the intrinsic capacitance of the handpiece and the internal resistance thereof, an RLC circuit close to the resonance is formed.